Enzymes are

Which of the following is a primary lymphoid organ?

What are the substances which mimic the natural chemical messengers?

As shown in the figure,charges $+q$ and $-q$ are placed at the vertices $B$ and $C$ of an isosceles triangle. The potential at the vertex $A$ is

If $\cos (x-y), \cos x, \cos (x+y)$ are three distinct numbers which are in harmonic progression and $\cos x \neq \cos y$,then $1+\cos y$ is equal to

Which of the following properties is $NOT$ exhibited by $Carbon$?